Electronic Design

Fiber Optics' Ascendance In Digital Transport Networks

Whenever a technology is in the early stages of evolution, a mélange of mostly uncoordinated changes involving specs and data rates, among others, is par for the course. Fiber-optic transport networks are no exception. They descended from T1/E1, which has become known as the first-generation Digital Transport Network T1/E1 (see the figure). Totally electrical, it was introduced in the 1960s. Fiber-optic digital transport arrived in the 1980s with the "second generation:" Sonet/SDH (synchronous and optical networks/synchronous digital hierarchy). We are talking about data rates of 51.84 Mbits/s in the U.S. and 155.52 Mbits/s in Europe.

Just what to call the third-generation digital-transport-network fiber optics is uncertain. Right now, the term optical transport network (OTN) is widely used. Whatever the moniker, it will unleash fiber-optic transport networks from many of their earlier constraints, such as static bandwidth on demand (BOD).

In fact, OTN with dynamic BOD has already hit the streets. We can expect full-fledged OTN with all the trimmings—advanced voice, video, data, tailored quality-of-service, and, of course, dynamic BOD—to be firmly in place by 2004.

Today, second-generation is principally O/E/O, which means optically accepted signals/electrically processed/optically sent to the next node. But all-optical, third-generation O/O/O is far from reaching commercial deployment on a mass scale.

Quite simply, the goal is to never convert back to electronic, which means start as O/O/O and keep going O/O/O—all the way. Then, convert to electrical once the destination has been reached.

What does this mean for those seeking to fulfill their fiber-optic digital transport requirements? It's a little like a floating craps game. Users looking to introduce products that are both technologically and economically competitive, and those developing instrumentation, must pay keen attention to the pace and nature of the evolution of digital transport networks. That's what it will take to be viable in the fiber-optic marketplace that awaits.

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